The orchestration of the temporal and spatial events responsible for proper cell division requires a host of proteins acting in concert to ensure that accurate mitotic progression occurs reproducibly. The focal point of this proposal is one such evolutionary conserved protein of unknown function termed NUD-1, a gene product that is essential for embryogenesis in the nematode model organism, C. elegans. Changes in protein levels of NUD-1 result in aberrant cell division, including a distinctive absence of midbody microtubules at anaphase during mitosis and loss of gamma-tubulin at centrosomes. Here we propose to further discern the functional relationship between NUD-1 and gamma-tubulin at the centrosome. Additionally, we will investigate the dependence of other centrosome-associated proteins on NUD-1 activity in vivo. Previous work has established that NudC, the mammalian homolog of NUD-1, is phosphorylated by the polo-like kinase Plk1, and that this interaction is necessary for the proper localization of Plk1 and progression through cytokinesis. It has been further demonstrated that Hsp90, a ubiquitous molecular chaperone, regulates Plk1 during mitosis and is required for Plk1 localization to centrosomes. Importantly, Hsp90 activity is dependent upon a co-chaperone termed p23, a protein that shares significant structural homology with NUD-1/NudC. We propose to investigate the possibility that Plk1-NudC interaction entails a regulatory mechanism involving Hsp90 to facilitate events essential to centrosome function in mitosis. Our approach employs a combination of RNA interference (RNAi), biochemistry, immunocytochemistry and fluorescent microscopy to gain a greater understanding of the molecular mechanisms by which NUD-1 and its partner proteins act in cell division, using the C. elegans one-celled embryo as a model system to investigate the detailed consequences of aberrant gene activity at the centrosome. Relevance to Public Health: The proposed proteins of study (NudC, Hsp90, and Plk1) are significant in various cancers including leukemia, breast, prostate and skin cancer. Additionally, prostate tumor growth can be inhibited by overproduction of NudC in prostate cancer cells in vitro. Elucidating the functional mechanisms mediated by these proteins in cell division provides a better understanding of the cancerous process, thereby contributing to the development of more defined avenues of therapeutic intervention. [unreadable] [unreadable] [unreadable]